Method of and apparatus for evaluating lost circulation materials



June 13, 1967 WATSON ET AL 3,324,71

' METHOD OF AND APPARATUS FOR EVALUATING LOST CIRCULATION MATERIALS Filed March 25. 1964 2 SheetsSheet l INVENTORS EDWARD HENRY NORMAN WATSON GEOFFREY HAMlLTON .SMITH BY MQRGAN, FINNEGAN, DURHAM 8| PINE ATTORNEYS June 13, 1967 H. N.WATSON ETAL 3,324,712

E. METHOD OF AND APPARATUS FOR EVALUATING LOST CIRCULATION MATERIALS Filed March 25. 1964 2 Sheets-Sheet 2 EDWARD HENRY NORMAN WATSON GEOFFREY HAMILTON SMITH BY MORGAN, FINNEGAN, DURHAM 8| PINE ATTORNEYS United States Patent Ofiice Patented June 13, 1967 3,324,712 METHOD OF AND APPARATUS FOR EVALU- ATING L051 CIRCULATION MATERIALS Edward Henry Norman Watson and Geoffrey Hamilton Smith, both of Sunbury-on-Thames, Middlesex, England, assignors to The British Petroleum Company Limited, London, England, a corporation of England Filed Mar. 25, 1964, Ser. No. 354,712 Claims priority, application Great Britain, Apr. 1, 1963, 12,784/ 63 7 Claims. (Cl. 73-61.4)

The present invention relates to a method of and apparatus for evaluating lost circulation materials.

When drilling for oil it is normal to circulate drilling mud down inside the drill string to the drill bit and up the bore hole to the surface. This mud facilitates cooling and lubrication of the drill bit and carries the drillings up to the surface of the bore hole. When a bore hole encounters a fracture or fissure, i.e., a wedge-shaped narrow opening, in the formations being drilled, some of the drilling mud passes into the fracture or fissure and is therefore lost.

This undesirable loss of drilling mud is overcome by including so-called lost circulation material, for example crushed walnut shells, as one of the constituents of the drilling mud. The lost circulation material flows with the drilling mud into any fissures or fractures and forms a sealing plug to block the flow of drilling mud into the formation.

Fractures in the formation being drilled may be natural fractures or may be induced fractures caused by the drilling operation. Both natural and induced fractures ar sealed during the drilling operation by normal lost circulation material. When drilling ceases the natural fractures remain stationary and the sealing plug is left in poistion. However induced fractures tend to close when the pressure causing them (due to drilling) is removed and the sealing plug tends to be forced back into the bore hole. When drilling is recommended the induced fracture again appears and has to be rescaled, more drilling mud being lost in the process.

It is an object of the present invention to provide a method of, and apparatus for, evaluating the suitability of lost circulation materials for sealing fissures, and natural and induced fractures of different dimensions.

According to one aspect of the present invention we provide an apparatus for evaluating the suitability of lost circulation materials for sealing fractures or fissures including a cell comprising a longitudinally extending body having a wedge-shaped slot therethrough, the cell being adjustable to vary the aperture of, and the slope through the wedge-shaped slot whereby fractures and fissures of varying dimensions can be simulated.

One wall of the wedge-shaped slot may be formed by a movable member to facilitate the said adjustment of the cell.

Means may be provided for applying pressure, in use, to the movable member, the pressure being applied in such manner that the wedge-shaped slot is tended to be closed, whereby the characteristics of an induced fracture can be simulated.

The surfaces of the walls of the wedge-shaped slot may be roughened to better simulate formation conditions.

A reservoir may be fitted to the end of the cell having the widest aperture of the wedge-shaped slot, the reservoir being such that, in use, drilling mud containing lost circulation material to be tested can be fed to the cell under pressure.

According to another aspect of the present invention we provide a method of evaluating the suitability of lost circulation materials, contained in a drilling mud, for effectively sealing an induced fracture in a formation being drilled, wherein the drilling mud is fed into the larger aperture of an open-ended wedge-shaped slot in a test cell until a sealing plug is formed in the slot by the lost circulation material, pressure then being applied to at least one of the walls of the wedge-shaped slot, the pressure tending to close the slot, the pressure then being removed from the wall or walls and further mud being fed into the larger aperture of the wedge-shaped slot to determine whether the previously formed sealing plug is still providing an effective seal.

In order that the invention can be more easily understood a specific embodiment thereof will hereinafter be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a sectional view of an apparatus according to the embodiment;

FIG. 2 shows a plan view of the apparatus of FIG. 1 looking in the direction of arrow X;

FIG. 3 shows a plan view of the apparatus of FIG. ltaken along the line AA;

FIG. 4 shows a plan view of the apparatus of FIG. 1 taken along the line BB;

FIG. 5 shows a schematic representation of the apparatus shown in the previous figures connected to a system for evaluating lost circulation materials.

Referring now to FIGS. 1, 2, 3 and 4 together there is shown a cell 11 based on a stand 12 and having a reservoir 13 mounted about it.

The cell 11 is cylindrical with a rectangular internal cross-section. Cell 11 is fabricated in two halves, which are held together by bolts 14 (FIG. 3), to allow the mounting of a movable beam 15.

The beam 15 is rigid and is connected at each of its ends to a pivotably mounted member 16 which is a sliding fit in a bush 17 fixed in the wall of the cell 11. A pair of springs 18 are positioned adjacent each end of the beam 15 arranged so as to hold the members 16 in contact with adjusting screws 9 thereby normally biasing beam 15 in a direction to increase the volume of slot 19. The position of each end of the beam 15 can be adjusted by adjusting screws 9, located in the bushes 17, which act on the members 16. The position of the beam 15 is adjusted to vary the slope and the size of opening to form a wedge-shaped slot 19 which runs the complete length of cell 11. The surfaces of the walls of the wedge-shaped slot 19 may be roughened to better simulate formation conditions. indicating members 29 are screwed into members 16 via slots 21 in bushes 17 to indicate the position of each end of the beam 15 on a graduated scale 22 on the bushes 17. O-ring seals 23 are positioned between the bushes 17 and the wall of cell 11, and between the members 16 and the bushes 17. These seals maintain a gas tight seal between the interior and exterior of the cell 11. A pressure inlet port 24 is positioned in the wall of the cell 11 such that gas pressure can be applied to the beam 15 in a direction opposing the action of the springs 18 the pressure chamber supplied by pressure inlet port 24 being on the side of beam 15 remote from the plane surface of the beam which, in part, defines slot 19.

The reservoir 13 comprises a cylindrical member 25 having a screw cap 26. The screw cap 26 has apertures 27 to accommodate a tommy bar (not shown) to facilitate screwing the cap into the member 25, an O-ring seal 28 being positioned between the cap 26 and the member 25 to ensure a fluid tight seal between them. A pressure inlet port 29 is positioned in the cap 26 to facilitate pressure to be applied to drilling mud contained in member 25, in use. A base plate 30 is screwed and welded to the bottom of the member 25. The base plate 30 has an aperture 31 which co-operates with and is of a size equal to the largest possible aperture of the top of the wedgeshaped slot 19 in the cell 11. The reservoir 13 is bolted, via its base plate 30, to the top of the cell 11 by bolts 32, a seal 33 being placed between them ensuring a fluid tight seal between cell 11 and baseplate 30, and the top surface of beam 15 and base plate 32.

The stand 12 comprises a member 34 which is bolted to the bottom of the cell 11 by bolts 35, a seal 36 being placed between them ensuring a fluid tight seal between cell 11 and member 34, and the bottom surface of beam 15 and member 34. The member 34 has an aperture 37 which co-operates with and is of a size equal to the largest possible aperture of the bottom of the wedge-shaped slot 19 in cell 11. A member 34 is supported on and bolted to, by bolts 38, a plate 39 having legs 46. A screw cap 41 is provided in the bottom of member 34, an O-ring seal 42 being positioned between them to ensure a fluid tight seal.

The method of operation of the apparatus will now be described with particular reference to FIG. 5. Beam 15 is adjusted to the required position by means of adjusting screws 9, the position of the beam being shown by indicating members 20. Reservoir \13 is then filled with drilling mud containing the lost circulation material to be tested, the caps 26 and 41 first having been removed. The apparatus is allowed to stand with the mixture flowing through aperture 31 into the wedge-shaped slot 19 through aperture 37 into a receptacle (not shown) heneath the stand. If the lost circulation material is etfective, a sealing plug is formed in the wedge-shaped slot 19 and mud ceases to flow into the receptacle.

When an effective seal has been formed in the wedgeshaped slot 19, the reservoir 13 is toppedup and the cap 26 replaced. Gas pressure is applied to the reservoir '13 via pressure inlet port 29 and via valve 42 in control panel 43 from a gas cylinder (no shown), valves 44 and 49, also in control panel 43, being closed. The gas pressure is then built up to a desired maximum (for example 50 lbs. per sq. in).

The assembly is left at this pressure for a predetermined time (for example 4 hrs.) by which time, if the seal is eflicient, clear filtrate is discharged from the slot 19 indicating that mud solids have bonded the lost circulation material successfully.

At this stage gas pressure is increased to 100500 psi. and the cell left in this condition for 16 hrs. approx.

If an effective seal has been attained the gas pressure is replaced by hydraulic pressure up to higher maximum value (for example 1000 lbs. per sq. in.). The hydraulic pressure is applied by pumping hydraulic fluid from a reservoir 45 by a pump 46 through valve 47 and control panel 43 into the pressure inlet port 29, valves 42, 44 and '49 in control panel 43 being closed. The pressure being applied to reservoir 13 is indicated by pressure gauge 48. A bleed valve 49 in control panel 43 is connected by a return pipe to the reservoir 45 from a fourway manifold 50. The cap 41 is placed in position during the application of hydraulic pressure so that if the seal plug breaks down the mhrture is still retained in the apparatus.

If the seal effectively withstands the applied hydraulic pressure this pressure is gradually removed and gas pressure is applied to the rear of beam 15 via pressure inlet port 24. The gas pressure is applied via valve 44 in control panel 43 from the gas cylinder, the valves 42 and 49 in control panel 43 being closed. The gas pressure is increased to predetermined maximum (for example lbs. per sq. in.). and maintained for a certain time (for example 30 mins.) after which it is released and the hydraulic pressure reapplied to the reservoir 13, as previously described, attempting to reach the predetermined maximum pressure. The hydraulic pressure is reapplied to determine if the sealing plug remains effective after the compression which simulates induced fracture conditions.

A material that satisfactorily plugs the slot under the above conditions is considered acceptable for sealing normal or induced fractures and fissures of the particular dimensions applied. Failure at any stage of the test is noted together with the pressure at which bearkdown occurs. The test is then resumed using the next smallest slot setting in order to determine the maximum fissure dimensions the material is capable of sealing.

We claim:

1. Apparatus for evaluating the ability of lost circulation materials to seal fissures in an earth formation comprising a test cell which includes an elongated body having a wedge-shaped slot extending axially therethrough to simulate a fissure, said slot being defined by at least two wall surfaces at least one of which can be positionally adjusted so as to vary the cross-section and wedge angle of said slot, and means coupled to said body for introducing drilling mud containing lost circulation material into the wider-apertured end of said slot to determine whether said lost circulation material seals the slot for a predetermined setting of the slot dimension.

2. Apparatus according to claim 1, in which said test cell includes a rigid movable member having a plane surface arranged to act as said adjustable wall surface and co-extensive with the length of the slot.

3. Apparatus according to claim 2, in which said means for introducing drilling mud and lost circulation material into said slot comprises a reservoir coupled to the end of said body defining said wider-apertured end of the slot, said reservoir being connectable to a source of pressurized fluid such that, in use, drilling mud containing lost circulation material can be fed to said slot under pressure.

4. Apparatus according to claim 2, which includes means defining a pressure chamber on the side of said movable member remote from said plane surface, means normally biasing said movable member in a direction to increase the volume of said slot, and stop means acting to lhnit movement of said movable member due to said biasing means, said chamber being connectable to a source of pressurized fluid so as to overcome said biasing means and tend to decrease the volume of said slot and compress any seal formed in said slot.

5. Apparatus according to claim 2, which includes movable elements coupled to said movable member adjacent to each end thereof, and indicating means linked to said movable elements and arranged to provide an indication of the dimensions of said slot at each end thereof.

6. Apparatus according to claim 1, in which said wall surfaces defining said slot are roughened to simulate the earth formation conditions.

7. A method of evaluating the ability of lost circulation materials contained in a drilling mud to seal :an induced fracture in an earth formation being drilled, which comprises the steps of feeding the drilling mud and lost circulation material into the larger aperture end of an open-ended wedge-shaped slot in a test cell until a sealing plug is formed in the slot by the lost circulation material, said slot being defined by at least two wall surfaces at least one of which can be positionally adjusted, applying pressure to said plug in the direction of the length of said slot to ensure that the plug can withstand a predetermined longitudinal pressure, applying pressure to said movable wall surface tending to close the slot, then removing the pressure from said movable wall surface, and again applying pressure to said plug in the direction of the length of the slot to determine whether the previously formed sealing plug is still providing an efiective seal.

References Cited UNITED STATES PATENTS 2,301,355 11/1942 Armentrout 138-45 5 2,733,595 2/1956 Twining 73-38 3,172,286 3/1965 Grubb et a1. '7353 3,180,825 4/1965 Couvreur et a1 210350 LOUIS R. PRINCE, Primaly Examiner.

10 D. M. YASICH, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,324 712 June 13 1967 Edward Henry Norman Watson et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 38, for "recommended" read recommenced column 2, line 35, for "about" read above column 3, line 59, for "500" read 150 column 4, line 7, for "predetermined" read a predetermined line 8, for "lbs. per sq. in.) read lbs. per sq. in.) line 20, for "bearkdown" read breakdown line 36, for "dimension" read dimensions Signed and sealed this 30th day of July 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. APPARATUS FOR EVALUATING THE ABILITY OF LOST CIRCULATION MATERIALS TO SEAL FISSURES IN AN EARTH FORMATION COMPRISING A TEST CELL WHICH INCLUDES AN ELONGATED BODY HAVING A WEDGE-SHAPED SLOT EXTENDING AXIALLY THERETHROUGH TO SIMULATE A FISSURE, SAID SLOT BEING DEFINED BY AT LEAST TWO WALL SURFACES AT LEAST ONE OF WHICH CAN BE POSITIONALLY ADJUSTED SO AS TO VARY THE CROSS-SECTION AND 